I can't say I"m an "expert." At this point I don't have kids, I have simply worked with them professionally and on a volunteer basis for 16 years and helped raise some cousins.
I really don't see a need for "this is now a prepping activity, lets go prep together..." type of approach with children. I think simply saying "hey, this is what mom and dad are doing, wanna help?" is going to get you the most mileage. More of a "let's do fun things together!" approach. If your preps are not too obvious and your language is not too extreme, then there is not as great a need for "opsec" either. If your children don't think of you as "being prepared" for anything more than common occurrences, there won't be much of an issue with training them to keep quiet about things, and that helps them develop more as children. Keeping secrets can be pretty hard on them. Feeling weird or unusual can also be tough.
And for the sake of everything good, don't have some sort of "now this is our food, and if Billy or Sally, or their parents come to take it, we might have to shoot them...." kind of conversation.
Frankly, I think the best way to go is to take them along on your own adventures (abroad and in the home) and make it fun.
I think the best opsec comes from their not knowing you are more prepared than your neighbors.
* Please remember: I'm just a guy on the internet
* Don't go to stupid places with stupid people and do stupid things.
*Be courteous. Look normal. Be in bed by 10'clock.
“It's a dangerous business, Frodo, going out your door. You step onto the road, and if you don't keep your feet, there's no knowing where you might be swept off to.” -Bilbo Baggins.